Chemical substance functional characterization

The Neurophysiology Sensory Evoked Potentials test guideline (OPPTS 870.6855) is designed to detect and characterize changes in the sensory aspects of nervous system function that result from exposure to chemical substances. The techniques involve neurophysiological measurements from adult animals and are sensitive to changes in the function of auditory, somatosensory (body sensation), and visual sensory systems. 

Once this function is determined, it could be applied to any substance, provided its critical constants Pc, T, and V are known. One way of applying this principle is to choose a reference substance for which accurate PVT data are available. The properties of other substances are then related to it, based on the assumption of comparable reduced properties. This straightforward application of the principle is valid for components having similar chemical structure. In order to broaden its applicability to disparate substances, additional characterizing parameters have been introduced, such as shape factors, the acentric factor, and the critical compressibility factor. Another difficulty that must be overcome before the principle of corresponding states can successfully be applied to real fluids is the handling of mixtures. The problem concerns the definitions of Pq P(> and Vc for a mixture. It is evident that mixing rules of some sort need to be formulated. One method that is commonly used follows the Kay s rules (Kay, 1936), which define mixture pseudocritical constants in terms of constituent component critical constants ... 

The scheme for the identification of an organic compound by chemical methods usually consists of the following stages (1) separation of an individual component or a group of individual components from a mixture (2) chemical conversion of an isolated fraction to produce substances that characterize the functional group composition of the... 

With a few exceptions, all infrared spectra of humic substances have been measured in dry solid samples, and the pressed-pellet method has been used almost exclusively. The spectrum of humic acid consists of relatively few bands that are very broad. The broadness of the bands reveals that humic substances are complex mixtures where a particular type of functional group can exist in a wide variety of chemical environments, each characterized by slightly different force constants for its bonds. Fourier-transform infrared (FTIR) spectroscopy allows the samples to be observed in their native wet state and avoids the shifts in chemical equilibrium which must necessarily accompany the drying process. 

The amount of component i in the gas phase is given by its partial pressure pi, which is a function of the properties of the component monitored and the properties of other, simultaneously present substances and also of the ambient temperature and pressure. The composition of a gas phase is characterized by great complexity (all the chemical substances have the final vapor pressure value regardless of their polarity), instability (slow reactions take place between oxidizing and reducing substances that are simultaneously present), and low concentration levels (frequently below the detection limit in the in situ state). In addition to gases, the gas phase also contains suspended particulate matter and solid dust particles. 

Microiontophoresis - The characterization of a transmitter function for a chemical substance also depends upon the demonstration that its physiologic effects and sensitivity to drugs are Identical to the natural transmitter. This statement implies that the putative transmitter substance is able to elicit some sort of physiologic response on the cell in question. In order to know this with certainty requires optimal physical resolution of the drug-neuron Interaction and discreteness in both the route of administration of the substances tested and the delineation of... 

The aroma of fmit, the taste of candy, and the texture of bread are examples of flavor perception. In each case, physical and chemical stmctures ia these foods stimulate receptors ia the nose and mouth. Impulses from these receptors are then processed iato perceptions of flavor by the brain. Attention, emotion, memory, cognition, and other brain functions combine with these perceptions to cause behavior, eg, a sense of pleasure, a memory, an idea, a fantasy, a purchase. These are psychological processes and as such have all the complexities of the human mind. Flavor characterization attempts to define what causes flavor and to determine if human response to flavor can be predicted. The ways ia which simple flavor active substances, flavorants, produce perceptions are described both ia terms of the physiology, ie, transduction, and psychophysics, ie, dose-response relationships, of flavor (1,2). Progress has been made ia understanding how perceptions of simple flavorants are processed iato hedonic behavior, ie, degree of liking, or concept formation, eg, crispy or umami (savory) (3,4). However, it is unclear how complex mixtures of flavorants are perceived or what behavior they cause. Flavor characterization involves the chemical measurement of iadividual flavorants and the use of sensory tests to determine their impact on behavior. 

The density of a material is a function of temperature and pressure but its value at some standard condition (for example, 293.15 K or 298.15 K at either atmospheric pressure or at the vapor pressure of the compound) often is used to characterize a compound and to ascertain its purity. Accurate density measurements as a function of temperature are important for custody transfer of materials when the volume of the material transferred at a specific temperature is known but contracts specify the mass of material transferred. Engineering applications utilize the density of a substance widely, frequently for the efficient design and safe operation of chemical plants and equipment. The density and the vapor pressure are the most often-quoted properties of a substance, and the properties most often required for prediction of other properties of the substance. In this volume, we do not report the density of gases, but rather the densities of solids as a function of temperature at atmospheric pressure and the densities of liquids either at atmospheric pressure or along the saturation line up to the critical temperature. 

Christensen, B. E. (1999). Physical and chemical properties of extracellular polysaccharides associated with biofilms and related systems. In Microbial Extracellular Polymeric Substances. Characterization, Structure and Function, eds. Wingender, J., Neu, T. R. and Flemming, H.-C., Springer-Verlag, Berlin, pp. 143-154. 

Now I would like to turn to some of the issues of operations within the manufacturing process itself and speak to certain process controls that are expected. In a chemical synthesis sequence, as I mentioned above, intermediates will need to be fully characterized. That characterization will then lead to a set of specifications for the intermediate, that is, its level of purity, its form, etc. Test procedures that demonstrate that the intermediate meets specifications must be established. Some intermediates are deemed to be more important than others and are given specific designation, such as pivotal, key, and final intermediates. In those cases, it is necessary to demonstrate that the specific and appropriate structure is obtained from the chemical reaction and that the yield of the intermediate is documented and meets the expected yield to demonstrate process reproducibility and control. Purity of the substance is to be appropriately documented. And, finally, in reactions which produce pivotal, key, and final intermediates, side products or undesirable impurities are identified and their concentrations measured and reduced by appropriate purification procedures so that the intermediate meets in-process specifications. Thus, those important intermediates become focuses of the process to demonstrate that the process is "under control" and functioning in a reproducible and expected manner. All of these activities ultimately are designed to lead to the production of the actual active ingredient which is referred to then as a "bulk pharmaceutical agent." That final product will need to be completely characterized which then will document that it meets a set of specifications ("Final Product Specifications") for qualification as suitable for pharmaceutical use. 

The production of substances with well-defined product properties under consideration of economical and ecological boundary conditions is the objective of many processes. For particulate materials, the product properties depend not only on the chemical composition but also on the dispersity of the material. The dispersity is characterized by the particle size distribution, the particles shape and morphology as well as their interfacial properties. This relation was called property function by Rumpf [1]. The control of the property function is known as product engineering or product design. 

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